1. Field of the Invention
This invention relates to electronic musical tone synthesis and in particular is concerned with tones having an extended number of harmonics.
2. Description of the Prior Art
A relatively large number of harmonics are required for an electronic tone synthesizer which imitates certain types of musical tones. These sounds include brass, strings, and reed families of tone. While the maximum harmonic capability of tone generation for almost any musical tone generator usually can be extended by adding to the number and size of the system elements, such a straightforward harmonic capability extension may not be economically feasible for a low cost musical instrument design. Increasing the maximum number of harmonics in a digital tone generation system may easily encounter a speed limitation imposed by the maximum clock speed at which the digital logic circuitry can be operated.
In U.S. Pat. No. 3,809,709 entitled "Implementation Of Combined Footage Stops In A Computor Organ" a method is disclosed for producing an approximation to a combination of tones at different fundamental frequencies during a single tone calculation algorithm which computes waveshape amplitudes by evaluating a discrete Fourier transform of a stored set of harmonic coefficients. The first tone is computed using an incomplete set of harmonics and a second tone, at lower pitch, is computed by using the first harmonic and some selected low order odd harmonics.
The present invention provides a novel implementation for extending the maximum harmonic capability of a digital musical tone generator.